Discover Copper Online

Spring 1998

Undersea Oil Platforms Rigged with Copper

It takes many tons of copper to tap the petroleum hidden under the oceans. Offshore drilling rigs bring up some 25% of all oil and 20% of all natural gas produced world­wide.

Rigs standing on the sea bottom in warmer climates rely on 90-10 copper-nickel sheathing on structural steel members in the exposed "splash-spray zone" (about 30 feet above and below average sea level). The biostatic sheathing repels marine organisms, which otherwise would form heavy encrustation that weigh down the rigs and increase the effective force of powerful waves and winds.

Without the sheathing, the steel structures would have to be much heavier and cost more. "The copper alloy sheathing is a long-term solution," according to Peter Haigh, senior engineer for the Asset Integrity Group of the British Gas Morcambe Field Management and Support Group, commenting on the performance of sheathing installed on its North Sea rigs 12 years ago. "We are very happy with it."

In addition to sheathing, there are many other applications of copper on the rigs. They include:

  • Copper-alloy piping or linings for piping made of other metals,
  • Big heat exchangers to cool the hot oil brought up from deep inside the earth,
  • Huge pumps made of copper alloys,
  • Scores of premium motors driving those pumps as well as cranes,
  • As many as four big generators driven by turbines fueled with natural gas from under the sea and providing as much as five megawatts of power - enough to supply a small city,
  • Some 100,000 feet of copper electrical cable connecting all the pumps and generators plus lighting and control computers

Communities of skilled workers inhabit the latest multistory rigs. Many rigs weigh 10,000 tons and more, are 120 to 180 feet high and can easily cost $200 million to construct, according to a spokesman for McDermott Engineering Hous­ton, a leading builder of rigs. The world's largest rig, now tapping the Hibernia field over 300 miles out into the Atlantic off Newfoundland, is a one-of-a-kind rig that weighs 1.25 million tons, stands 733 feet high and cost $1 billion. Huge pumps on the rigs inject seawater into deep wells to bring up any residual oil left after the natural gas (used to push up the initial oil flow) fizzles away. Other pumps transfer the oil itself through underwater pipelines either to storage tanks on land or into tankers moored nearby.

According to David Medley, manager of the company's Design Alloys Division, high-pressure fitting blocks for seawater piping systems are forged out of ingots of C63000 nickel-aluminurn-bronze supplied by Ampco Metal, Inc., Milwaukee.

Many suppliers in addition to Ampco provide copper and its alloys and the components made of them to builders of rigs. For instance, Ansonia Copper & Brass supplies seamless piping for fire-protection systems made of 90-10 copper-nickel, C70600. Ansonia also supplies manufacturers of fittings for the fire-protection sys­tems with the same alloy. Hussey Marine Alloys supplies forged-and-machined flanges for the copper-alloy piping on rigs. The flanges are made of C70600 and 70-30 copper nickel, C71500.

There are heat exchangers on rigs to cool the hot oil gushing up from below the seabed. Revere Copper Products supplies the flat sheets into which are inserted the tubes carrying the seawater that cools the oil pouring over the tubes. The sheets, which range from one to four inches in thickness, are made of C61400 aluminum bronze and the C70600 or C71500 alloys. Wolverine, Inc., is a major supplier for the tubing, which is mostly made of C68700 aluminum bronze, C70600 and C71500. Hussey Copper, Ltd., Revere and the Olin Corporation make the 90-10 copper-nickel sheathing.

Ampco: 414/645-3750
Ansonia: 800/521-1703
Hussey: 800/767-0550
Olin: 618/258-2000
Revere: 800/831-1801
Scot Forge: 847/587-1000
Wolverine Tube: 800/633-3972

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